A tile adhesive blend is mixed with water to make a workable paste which is useful as a tile adhesive to glue tiles to a surface. The adhesive becomes hard when it sets, resulting in a rigid aggregate structure.
Present-day, cement based tile adhesives are typically made from a mixture of an aggregate such as sand, a binder such as Portland cement, aluminate cement or lime, and water. Commonly, a tile adhesive blend consists of about 28 weight %-32 weight % of cement and of about 65 weight %-70 weight % of aggregate. The rest are admixtures and fibre chemicals. Just before use, the tile adhesive is mixed with water. The tile adhesive blend is stored dry in bags.
Cement is thus used as the binder material that hardens to form the connecting material between solids. Cements that are used in construction are either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, being a chemical reaction between anhydrous cement powder and water. Consequently, they can harden underwater or when constantly exposed to wet weather. The chemical reaction results in hydrates that are not very water-soluble and so are quite durable in water. Non-hydraulic cements do not harden underwater. Slaked limes for example harden by reaction with atmospheric carbon dioxide. Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to a temperature of 1450° C. in a kiln, in a process known as calcination. In a calcination process, a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, also called quicklime, which is then blended with the other materials that have been included in the mix. The resulting hard substance, called ‘clinker’, is then ground with a small amount of gypsum into a powder to make ‘Ordinary Portland Cement’, the most commonly used type of cement (often referred to as OPC).
There exist different types of cement, within CEN region (Europe) indicated with CEM I to CEM V, with a lower or higher content of Portland cement                CEM I: OPC with maximally 5% of other compounds;        CEM II: all kinds of mixtures of OPC and for instance slate, minimally 65% OPC;        CEM III: high oven/Portland cement mixture in 3 classes: A, B and C, wherein CEM III/A comprises the lowest (40%) and CEM III/C the highest (60%) amount of blast furnace slag;        CEM IV: types of Pozzolana cement;        CEM V: composite cements, with mixtures of OPC, blast furnace slag and Pozzolana compounds.        
Another option is the classification according to ASTM standards, where mostly the ASTM type I and I/II class are high Portland cement content cements.
For tile adhesives, commonly only CEM I or ASTM type I is used, but due to its globally decreasing availability in favour of CEM II classes, there might be a change.
As tile adhesives are commonly used indoors, there is no strong dependency towards climate. However, a setting accelerator is often used in order to increase the performance of tile laying.
Until now, the most commonly used setting accelerator for tile adhesive blends is calcium formate (Ca(HCOO)2). Calcium formate is a non-hygroscopic powder that shows good response with Ordinary Portland Cement (OPC). The disadvantage of calcium formate however is that it shows a weak response on the more and more popular blended cements like CEM II/A-V. In addition, calcium formate is quite an expensive calcium salt.
Calcium chloride (CaCl2), which is the most cost efficient calcium salt, can also be used as a setting accelerator. However it can lead to efflorescence as crystalline deposits on surfaces. As tiles might be exposed to humidity, this efflorescence can happen at the gaps and reduce visual quality. In addition tile adhesives are often put directly on concrete (especially walls and floors) and thus chloride might migrate into the structure and cause corrosion. Also metal tubing is in contact with the tile adhesives and can cause corrosion.
Calcium nitrate (Ca(NO3)2) is commonly used as a concrete admixture, usually in the form of a solution. The final liquid product for end users is prepared from either a solution or a dissolved powder, granules or prills. The calcium nitrate is not present in the prior art dry concrete blends as a powder, but is added as an aqueous solution after the concrete blend has been mixed with water. Common types of calcium nitrate powder is not used in dry concrete blends since they tend to promote clogging/caking of the blend, both during storage and final mixing with water. Calcium nitrate shows a good response on most blended cement types. Usually 1% to 2% calcium nitrate needs to be added by weight of cement (=bwoc). Calcium Nitrate does not provoke any corrosion and is economically in favour of Calcium Formate.
Therefore, there exists the need to provide a tile adhesive blend containing calcium nitrate powder which does not clog or cake and in which the calcium nitrate does not precipitates when being mixed with water. A further need is to provide a tile adhesive which is odor free when being processed.